Your body's immune system has several defensive ploys to attack and destroy unwelcome and potentially harmful microscopic invaders. The first defense is the skin and lining of organs that connect with the outside. These contain chemicals that break down unwelcome organisms. If an organism somehow sneaks past the skin barrier, your immune system then mobilizes a host of other defenses. Some cells surround the organisms while other cells, usually white blood cells called neutrophils, leave the blood vessel and enter the site of injury or infection. Now, other bacteria-eating cells called macrophages, travel to the injured site. They extend tentacle-like arms that reach out and snare the invading organism. The macrophage then destroys the microbe with powerful chemicals or swallows it whole. Macrophages, neutrophils, and skin, along with other immune components such as antibodies, provide a multi-faceted defense against infection.